Which of the following types of signal has the narrowest bandwidth?
The correct answer is C: CW. CW (Continuous Wave, Morse code) has the narrowest bandwidth of the listed signal types. CW signals are essentially unmodulated carriers that are keyed on and off, requiring only the bandwidth needed for the keying speed (typically 100-200 Hz for normal speeds). For amateur radio operators, CW's narrow bandwidth makes it excellent for weak-signal work, DX operation, and situations where bandwidth is limited. It's the most spectrum-efficient mode, allowing many stations to operate in a small frequency range.
Exam Tip
CW = narrowest bandwidth. Think 'C'W = 'C'ontinuous 'W'ave = 'C'ompact 'W'idth. CW uses only 100-200 Hz, making it the narrowest. FM (~15 kHz) and SSB (~3 kHz) are much wider.
Memory Aid
"CW = narrowest bandwidth. Think 'C'W = 'C'ontinuous 'W'ave = 'C'ompact 'W'idth (~150 Hz). Narrowest of all modes. FM (~15 kHz) and SSB (~3 kHz) are much wider."
Real-World Application
On a crowded band, CW operators can fit many stations in a small frequency range because each CW signal uses only about 150 Hz. In the same space, you might fit only one FM signal (15 kHz) or a few SSB signals (3 kHz each). CW's narrow bandwidth makes it ideal for weak-signal work and efficient spectrum use.
Key Concepts
Why Other Options Are Wrong
Option A (FM voice): Incorrect. FM voice requires about 15 kHz bandwidth, much wider than CW. FM's wide bandwidth provides good audio quality but uses more spectrum.
Option B (SSB voice): Incorrect. SSB voice requires about 3 kHz bandwidth, wider than CW. SSB is efficient but not as narrow as CW.
Option D (Slow-scan TV): Incorrect. Slow-scan TV requires several kHz of bandwidth, much wider than CW. Video signals need significant bandwidth.
题目解析
The correct answer is C: CW. CW (Continuous Wave, Morse code) has the narrowest bandwidth of the listed signal types. CW signals are essentially unmodulated carriers that are keyed on and off, requiring only the bandwidth needed for the keying speed (typically 100-200 Hz for normal speeds). For amateur radio operators, CW's narrow bandwidth makes it excellent for weak-signal work, DX operation, and situations where bandwidth is limited. It's the most spectrum-efficient mode, allowing many stations to operate in a small frequency range.
考试技巧
CW = narrowest bandwidth. Think 'C'W = 'C'ontinuous 'W'ave = 'C'ompact 'W'idth. CW uses only 100-200 Hz, making it the narrowest. FM (~15 kHz) and SSB (~3 kHz) are much wider.
记忆口诀
CW = narrowest bandwidth. Think 'C'W = 'C'ontinuous 'W'ave = 'C'ompact 'W'idth (~150 Hz). Narrowest of all modes. FM (~15 kHz) and SSB (~3 kHz) are much wider.
实际应用示例
On a crowded band, CW operators can fit many stations in a small frequency range because each CW signal uses only about 150 Hz. In the same space, you might fit only one FM signal (15 kHz) or a few SSB signals (3 kHz each). CW's narrow bandwidth makes it ideal for weak-signal work and efficient spectrum use.
错误选项分析
Option A (FM voice): Incorrect. FM voice requires about 15 kHz bandwidth, much wider than CW. FM's wide bandwidth provides good audio quality but uses more spectrum. Option B (SSB voice): Incorrect. SSB voice requires about 3 kHz bandwidth, wider than CW. SSB is efficient but not as narrow as CW. Option D (Slow-scan TV): Incorrect. Slow-scan TV requires several kHz of bandwidth, much wider than CW. Video signals need significant bandwidth.
知识点
CW bandwidth, Morse code, Narrow bandwidth, Spectrum efficiency
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.